================================================================================
expressions
================================================================================
a = 3 * (2 - 5)
b = . - a
	.long	.L71-.L6
c=3+b
--------------------------------------------------------------------------------
(source_file
  (assignment
    (symbol)
    (expression
      (number)
      (expression
        (number)
        (number))))
  (assignment
    (symbol)
    (expression
      (symbol)
      (symbol)))
  (directive
    (directive_name)
    (expression
      (symbol)
      (symbol)))
  (assignment
    (symbol)
    (expression
      (number)
      (symbol))))
